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The Thorax and its contents
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RESPIRATORY PHYSIOLOGY
The Thorax and its contents
◦Ventilation: Action of breathing with muscles and
lungs◦Gas exchange: Between air and capillaries in the lungs. Between systemic capillaries and
tissues of the body
Respiration
Gas Exchange◦ O2, CO2
Acid-base balance◦ CO2 +H2O←→ H2CO3 ←→ H+ + HCO3-
Phonation Pulmonary defense Pulmonary metabolism and handling of bioactive materials
Inspiration:lung volume increases ->
◦decrease in intrapulmonary pressure, to just below atmospheric pressure ->
◦air goes in!Expiration: vice versa
Compliance: ◦ This the ability of the lungs to stretch during
inspiration ◦ lungs can stretch when under tension.
Elasticity: ◦ It is the ability of the lungs to recoil to their
original collapsed shape during expiration◦ Elastin in the lungs helps recoil
Inspiration – Active process Diaphragm contracts -> increased
thoracic volume vertically. Intercostals contract, expanding rib cage
-> increased thoracic volume laterally. More volume -> lowered pressure -> air
in. Negative pressure breathing
Expiration – Passive◦Due to recoil of elastic lungs.◦Less volume -> pressure within alveoli is
just above atmospheric pressure -> air leaves lungs.
◦Note: Residual volume of air is always left behind, so alveoli do not collapse.
Conducting zone: Includes all the
structures that air passes through before reaching the respiratory zone.
Mouth, nose, pharynx, glottis, larynx, trachea, bronchi.
Conducting zone Warms and humidifies until inspired air
becomes:◦37 degrees◦Saturated with water vapor
Filters and cleans:◦Mucus secreted to trap particles ◦Mucus/particles moved by cilia to be
expectorated.
Respiratory zone
Region of gas exchange between air and blood
- Respiratory bronchioles- Alveolar ducts, Alveolar Sacs and- Alveoli
Air duct
Air Sac
Alveoli◦Air sacs◦Honeycomb-like clusters◦~ 300 million.
Large surface area (60–80 m2).◦Each alveolus: only 1 thin cell layer.◦Total air barrier is 2 cells across (2 m)
(alveolar cell and capillary endothelial cell).
◦Alveolar cells
◦Alveolar type I: structural cells.
◦Alveolar type II: secrete surfactant.
Respiratory Zone
Mechanical process that moves air in and out of the lungs.
Diffusion of… O2: air to blood. C02: blood to air. Rapid:
◦ large surface area ◦ small diffusion
distance.
19
Insert 16.1
Alveolar capillary interface
Alveolar capillary interface
Cellular Respiration
◦Oxygen: large “reservoir” attached to hemoglobin.
◦So chemoreceptors are more sensitive to changes in PC02
(as sensed through changes in pH).
◦Ventilation is adjusted to maintain arterial PC02 of 40 mm Hg.
◦Chemoreceptors are located throughout the body (in brain and arteries).
Affinity between hemoglobin and 02: pH falls -> less affinity -> more unloading (and vice versa if pH increases)
temp rises -> less affinity -> more unloading
exercise, fever
C02 transported in the blood: ◦- most as bicarbonate ion (HC03
-)◦- dissolved C02
◦- C02 attached to hemoglobin (Carbaminohemoglobin)
• Carbonic anhydrase in RBC promotesuseful changes in blood PC02
H20 + C02 -> H2C03 -> HC03-
high PC02
CA
H20 + C02 <- H2C03 <- HC03
- low PC02
CA
Normal blood pH: 7.40 (7.35- 7.45)
Alkalosis: pH up Acidosis: pH down
H20 + C02
Hypoventilation: ◦ PC02 rises, pH falls (acidosis).
Hyperventilation: ◦ PC02 falls, pH rises (alkalosis).
H2C03 H+ + HC03-
Ventilation is normally adjusted to keep pace with metabolic rate, so homeostasis of blood pH is maintained.
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